REFLECTOR: Shimmy and flutter thoughts.

michalk michalk at awpi.com
Fri Nov 18 12:40:31 CST 2005 

I might be able to do that tonight.

It's not going to be a weight, rather a moment-arm.  The farther out 
front, the less weight required.

I've thought that if someone wanted to make a superfast velocity, they'd 
have to do the same thing for the winglets.  To keep them from 
fluttering, the CG would need to be in front of the CL, make sure the 
rudders are stable too, then it might be possible to set them at a less 
draggy angle.

While I am at it, I would also remove the elevators from the canard and 
make it a flying elevator/canard.  If they want to use the Velocity for 
a rocket platform, I bet these are going to have to be done.

Also... I bet that we will also see a bulkhead like in the original 
Velocity design aft of the pilot/copilot seats that carries tension from 
the strakes to keep the wings from bending back, and pulling the 
fuselage into an oval.  Talk about a strong solution for a very 
lightweight spar.

I wish I knew something about aeronautics.  I could be dangerous.

Ron Brown wrote:
> I'm pretty certain the rod projects forward - to counterbalance the 
> weight behind the pivot that the fork, wheel and tire has.
> 
> Any body who hasn't installed their nose wheel and tire - could you 
> weigh the wheel and tire to give me an idea of how much mass needs to be 
> placed out front.
> 
> I'm guessing that nose wheel shimmy is similar to control surface 
> flutter. The likelihood of shimmy would be reduced/eliminated by having 
> the counterbalance equal or heavier than the tire and wheel.
> 
> Ronnie
> 
> ----- Original Message ----- From: "Chuck Jensen" <cjensen at dts9000.com>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Friday, November 18, 2005 8:16 AM
> Subject: RE: REFLECTOR: Shimmy and Nose Gear Pivot Bushings
> 
> 
> Ronnie,
> 
> The photo wasn't a detailed as one would like but I'm estimating that's
> a $50,000 to $75,000 military mod.  Of course, if the bolts that hold it
> on weren't bought at Home Depot, then it's probably more.
> 
> Alex had a good question about whether it's a trailing or leading mass,
> though it may not make a difference.  If trailing works, and if a 6" rod
> with a 2-3 pound mass of lead on the end of it would do the trick,
> wouldn't that be great.  If it's out front, a person would have to do
> some measuring and calculation for dog house clearance, but in the
> trailing position, it would look better and have lots of clearance.
> 
> Do we have any guinea pigs in the house?
> 
> Chuck
> 
> 
> 
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
> Behalf Of Ron Brown
> Sent: Thursday, November 17, 2005 6:13 PM
> To: Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings
> 
> Brian,
> 
> I did a Google on "nose wheel shimmy" and got the following article on
> F-15's and a fix for their long standing problem.  See
> http://engineering.wpafb.af.mil/success/F-15_Nose_Wheel_3_08_01.pdf
> 
> It involves what looks like a mass weight attached such that the center
> of
> mass is shifted forward.  Looks like something worth trying assuming
> there
> is room for the bar when the gear is up - I think there is.
> 
> It sure would be nice to be able to reduce the shimmy nut torque to
> something like 5-10 ft lbs instead of the difficult to steer 20 ft lbs.
> 
> Ronnie
> 
> ----- Original Message ----- From: "michalk" <michalk at awpi.com>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Tuesday, November 15, 2005 11:19 AM
> Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings
> 
> 
>> I always wondered why there hasn't been an example where a
> 
> counterbalance
> 
>> was used?
>>
>> The problem is that the CG is aft of the pivot point.  If one needs to
> 
> use
> 
>> ballast anyway, place a counterbalance to get the CG closer to the
> 
> pivot
> 
>> point.
>>
>> Might be a problem with RG's, maybe easier with fixed gear.  Get the
>> center of lift to be aft of pivot as well and have self centering
>> nosewheel, with a very light easy to steer friction system.
>>
>> Ron Brown wrote:
>>
>>> I discovered how destructive nose wheel shimmy can be.
>>>
>>> On a half dozen or so occassions, I have had nose wheel shimmy after
>>> landing.  The last time, I smelled hot epoxy.  After shut down I did
> 
> some
> 
>>> investigating and found that the right side pivot bushing had worked
>>> loose from its mounting in the keel. It had worn the hole into an egg
> 
> 
>>> shape with most of the wear toward the lower front of the bushing
>>> mounting.
>>>
>>> I have epoxied a new bushing into place using the Aeropoxy structural
> 
> 
>>> adhesive.
>>>
>>>> From now on, I am going to keep my bellville washers clean and
> 
> tighter
> 
>>>> to
>>>
>>>
>>> minimize - or rather prevent nose wheel shimmy.  (sure makes steering
> 
> 
>>> tougher - especially on take off)
>>>
>>> Has anybody else had this problem?  I am guessing there is a problem
> 
> in
> 
>>> that there is a new and improved mounting for these bushings.
>>>
>>> Do I also need to go ahead and plan to replace these with the new
>>> bushings and plates that are shown in the latest on-line plans?
>>>
>>> Ronnie
>>> 173 Elite RG
>>>
>>>
>>>
>>> (173 Elite RG).
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>>
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